Process and apparatus for cutting or welding a workpiece

ABSTRACT

A metal jet cutting system, which includes a jetting heat, a heater and a power source, is used for modifying a workpiece. The jetting head includes a crucible and an inlet for receiving a feed stock of a conductive material. The heater melts the conductive material in the crucible to provide a conductive fluid, which exits the jetting head via an outlet. The power source, which is in electrical communication with the conductive fluid, increases the temperature of the conductive fluid. The conductive fluid is applied to the workpiece to modify the workpiece.

RELATED APPLICATIONS

[0001] This application claims priority to and incorporates herein byreference in its entirety U.S. Provisional Application Serial No.60/155,078, filed Sep. 21, 1999, entitled Process and Apparatus ForCutting Or Welding A Workpiece.

FIELD OF THE INVENTION

[0002] The invention relates to a process and an apparatus for cuttingor welding a workpiece.

BACKGROUND OF THE INVENTION

[0003] Oxyfuel cutting, plasma cutting, and laser cutting are threeprincipal methods used to thermally cut a metallic workpiece. Oxyfuelcutting is mainly used to cut mild steel where the benefits of theexothermic burning reaction of oxygen and iron are used to do thecutting. In this process, the reaction rate and the resulting cuttingrate is determined by the diffusion rates of the reactants and the shearof the gas jet on the liquid metal to remove it from the cut. Forcutting a mild steel workpiece having a thickness in the range fromabout 10 mm to about 12 mm, typical cutting speeds range from about 0.5to about 1.5 meters/minute. Kerf widths vary from about 1 mm to greaterthan about 3 mm.

[0004] In plasma cutting, the energy used to cut a workpiece is suppliedby an electric-arc-heated plasma gas jet which is directed toward orbrought in contact with the workpiece. The plasma cutting techniqueworks on all types of electrically-conductive materials and, therefore,has a wider application range than oxy-fuel cutting. Typical plasma arctemperatures are greater than 6000° C. During plasma cutting, metal fromthe workpiece is removed from the kerf by the shear of the very highvelocity plasma-arc jet. Typical cutting speeds for plasma cutting aregreater than those of oxyfuel cutting A typical cutting speed forcutting ½″ mild steel with oxy-fuel is about 16 inches/min; whereas a200 Amp plasma system would typically cut that same size material at 80inches/min. Kerf widths for plasma cutting are about the same size orlarger then those for oxyfuel cutting. The relatively large kerf widthhas an adverse influence on the precision of the plasma cutting process.

[0005] In laser cutting, the energy used to cut a workpiece is suppliedby a laser beam directed toward or brought in contact with theworkpiece. Material is removed from the kerf by the shear from an assistgas jet directed into the kerf. In laser cutting, kerf widths arenarrow. Kerf widths typically range from about 0.15 mm to about 0.5 mm.These narrow kerf widths consequently yield higher precision cuttingthan is possible with either oxyfuel or plasma cutting. However, inlaser cutting, it becomes difficult to remove the molten metal from thekerf as the workpiece thickness increases. This limits the cutting speedand the maximum thickness capability for laser cutting. It is believedthat the reason for this limitation is that the high gas velocityrequired to achieve sufficient gas shear creates supersonic shock wavesa few millimeters into the kerf. These shock waves limit the gas shearand its ability to remove metal.

[0006] A fourth method for thermally cutting a workpiece is disclosed inU.S. Pat. No. 5,288,960. In this thermal-cutting method, a hightemperature liquid metal stream is directed at and impinges on theworkpiece. The temperature of the stream exceeds the melting temperatureof the workpiece. The problem of removing the molten metal from the kerfbecause of limited gas shear encountered in laser cutting is thus easedby using a medium (i.e., liquid) with a higher specific density.Compared to laser cutting, higher cutting speeds, thicker workpiececapability, and equivalent high precision cuts can be realized with thisliquid-metal-stream cutting approach. However, because of the need tosupply a high speed liquid stream to the workpiece, at a temperaturegreater than the workpiece melting point, this approach has been limitedin its use for cutting certain metal. The material requirements for ahigh temperature, high pressure, liquid containment vessel severelylimits the practicality of cutting metals such as aluminum, stainlesssteel and mild steel, where typical melting temperatures are 660° C.,1400° C. and 1550° C., respectively.

[0007] Several methods are used to thermally weld a workpiece. The mostwidely used welding processes use heat sources to cause localizedheating of two or more workpieces, allowing them to melt and flowtogether. A filler metal generally is added to the weld area in order tosupply sufficient material to fill the joint and to increase mechanicalstrength. For example, a fillet weld generally forms a radial sector ofadditional material over a weld groove when completed. When the weldingprocess is progressing, a molten pool of workpiece forms and a fillermaterial is moved along the welding front. When the welding heat sourceis removed, the molten metal solidifies, and the parts are fused orwelded together. Common heat sources used to provide heat to melt theworkpieces are DC or AC electrical arc, oxy-fuel gas flame, and laserbeam.

SUMMARY OF THE INVENTION

[0008] An objective of this invention is to provide a very high energydensity fluid stream which can be used in materials working processes.Another objective of this invention is to provide a process and anapparatus for thermally cutting workpieces at high speed and highprecision over a large range of workpiece thicknesses. Another objectiveof this invention is to provide a process and an apparatus for thermallywelding workpieces at high speed and high precision. Another objectiveof this invention is to thermally cut and/or weld non-metallic and/ornon-conducting materials. A further objective of this invention is toprovide a process and an apparatus of cutting and/or welding which issimple in design, easy to operate and maintain and cost effective touse.

[0009] In one aspect, the invention features a system for modifying aworkpiece. The system comprises a dispenser and a power source. Thedispenser comprises an electrically conductive material for forming ajet stream. The power source is electrically coupled to the jet stream.

[0010] In one embodiment, the dispenser comprises a jetting head. Forexample, the jetting head can comprise a crucible. A heater can becoupled to the crucible. The heater can comprise one of an AC resistanceheater, a DC resistance heater, an induction heater, or a combustionburner-heater arrangement. The heater can comprise an induction heatercoil wrapped around the crucible. In one example, the induction heatercoil wrapped around a first end of the crucible has a closer packedrelationship than the induction coil wrapped around a second end of thecrucible. In another example, the induction heater coil wrapped around afirst end of the crucible has a smaller diameter than the induction coilwrapped around a second end of the crucible. The system can furthercomprise a depressurizing vent in communication with the pressurecontainment vessel. The crucible can comprise a refractory material. Forexample, the crucible can comprise a material selected from one ofzirconium diboride, alumina, zirconia, boron nitride, and graphite. Theconductive material for forming the jet stream can comprise a metal.

[0011] The jetting head can comprise an inlet for receiving a feed stockof the conductive material. In another embodiment the jetting head cancomprise multiple inlets for receiving multiple feed stocks ofconductive material. The jetting head can further comprise a feed stockvalve. The jetting head can comprise a pressure containment vessel and aheater disposed inside the pressure containment vessel. The system canfurther comprise a pressurizing gas source in communication with thepressure containment vessel. The jetting head can comprise an electrodedisposed inside the crucible for establishing an electrical connectionwith the jet stream.

[0012] The jetting head can comprise an exit orifice. In addition, thejetting head can further comprise a plug. In this embodiment, thejetting head can comprise a plug rod disposed above the exit orifice.The jetting head can further comprise a nozzle. The nozzle can comprisea disk having a conical opening. The jetting head can further comprise anozzle and a nozzle cap detachably attached to the pressure containmentvessel adjacent the nozzle. In one embodiment a filter can be placed inseries with the nozzle. In another embodiment the crucible has aconductive fluid filter.

[0013] In one embodiment, the system for modifying a workpiece furthercomprises a first lead electrically coupled to the power supply and awork piece and a second lead electrically coupled to the power supplyand a conductive fluid disposed in the crucible. In another embodiment,the system of can further comprise a first lead electrically coupled tothe power supply and a work piece clamp and a second lead electricallycoupled to the power supply and a conductive fluid disposed in thecrucible. In still another embodiment, the system can further comprise afirst lead electrically coupled to the power supply and a currentcollector. For example, the current collector can comprise a vessel.

[0014] In still another embodiment, the system can further comprises afirst lead electrically coupled to a first power supply and a firstfeedstock and a second lead electrically coupled to the first powersupply and a second feedstock. The first and second feedstocks makingelectrical contact with the conductive fluid disposed in the crucible.The two feedstocks are heated by passing current between them. A secondpower supply comprises a first lead electrically coupled to the workpiece and a second lead electrically coupled to the power supply and afeedstock of the first power supply.

[0015] The jetting head can further comprise a shield assemblysupporting the nozzle. The shield assembly can comprise a disk having aplurality of inlet orifices for introducing a shield gas to the jetstream.

[0016] In another aspect, the invention features a metal jet cuttingsystem. The system comprises a jetting head including an exit orificefor dispensing a jet stream of a conductive fluid and a power sourceelectrically coupled to the jet stream for providing a current to thejet stream to increase a temperature of the jet stream above a meltingtemperature of the conductive fluid.

[0017] In still another aspect, the invention features a process formodifying a workpiece. According to the process, a jet stream comprisinga conductive fluid is provided. An electrical current is passed throughthe jet stream. The jet stream is directed at the workpiece formodifying the workpiece.

[0018] The jet stream can be heated in a variety of ways. A current canbe applied to the jet stream through an electrode coupled to theconductive fluid and a current collector disposed near the workpiece. Acurrent can be applied to the jet stream through an electrode coupled tothe conductive fluid and a workpiece clamp. The jet stream can be heatedthrough ohmic power dissipation. The jet stream can be heated to atemperature substantially above a melting temperature of the conductivefluid. A temperature of the jet stream can be increased up to about1000° C. above a melting temperature of the conductive fluid. The jetsteam can be a continuous jet stream, a pulsed jet stream, a steady jetstream, or an unsteady jet stream.

[0019] In one embodiment the heater of the crucible is an inductionheater where the characteristic frequency of the induction heater can becalibrated to the level of a conductive fluid in the curcible.

[0020] In one embodiment, the feed stock and the workpiece comprise thesame type of material. Alternatively, the feed stock can the workpiececan comprise different types materials. For example, the feed stock cancomprise aluminum and the workpiece can comprise stainless steel. Thefeed stock can be a conductive fluid. Alternatively, the feedstock canbe heated to form a conductive fluid. In one example, the feed stock isa metal such as aluminum, iron, an iron containing compound, tin,nickel, titanium, gold, platinum, silver, magnesium, copper, mild steelor aluminum-iron alloy. The feed stock can comprise a wire, bar, orpowder. In still another embodiment the feedstock can comprise a wire orbar and also serve as an electrical contact between a power source andthe conductive fluid. More than one feed stock can be in contact with anelectrical power source. The feed stock can comprise a plurality ofnon-melting particles. The non-melting particles can be abrasive. Thefeed stock can have a low melting point and a high boiling point.

[0021] The exit orifice of the crucible can be plugged while providingthe feed stock and the exit orifice can be unplugged while theconductive fluid passes through the exit orifice. A vacuum can beprovided to the jetting head to plug the exit orifice. A levitationforce can be provided to the conductive fluid to plug the exit orifice.

[0022] In one embodiment, the jetting head is pressurized while passingthe conductive fluid through the exit orifice. For example, the jettinghead can be pressurized by supplying an inert gas.

[0023] In another aspect, the invention features a crucible for a metaljet cutting system. The crucible comprises side walls and a base. Thecrucible is electrically conductive and is resistant to dissolving inthe presence of a metallic melt. The crucible can be formed from azirconium containing compound. The crucible can also be formed fromzirconia diboride or yitria-stabilized-zirconia.

[0024] In another aspect, the invention features a nozzle for a metaljet cutting system. The nozzle comprises a disk-structure having anorifice, wherein the orifice is located at a center of thedisk-structure. The nozzle is electrically conductive and is resistantto dissolving in the presence of a metallic melt. The nozzle can beformed from a zirconium containing compound. The nozzle can also beformed from zirconium diboride.

[0025] Various parameters can be controlled when the process of thepresent invention is performed. For example, a pressure in the jettinghead, a temperature of the conductive fluid, a depth of penetration ofthe jet stream and/or a velocity of the jet stream can be controlled.

[0026] In one embodiment, the workpiece can be cut, marked or pierced.Alternatively, the workpiece can be welded. For example in welding, afirst workpiece having a first tapered edge and a second workpiecehaving a second tapered edge are provided. The first tapered edge ispositioned adjacent the second tapered edge to provide a groove. The jetstream is directed at the groove to fill the groove. Directing the jetstream at the groove can melt a portion of the workpiece forming amolten pool in the groove. Cooling the molten pool welds the firstworkpiece and the second workpiece.

[0027] In one embodiment, a workpiece can be modified by lowering amelting point of the workpiece. The melting point can be lowered byforming an alloy of the feed stock material and the workpiece materialon a surface of a portion of the workpiece. The process of modifying aworkpiece can further include providing a shielding gas to shield thejet stream.

[0028] In one embodiment, the process of modifying the workpiece can beused to modify an insulative material. When modifying an insulativematerial, a current collector comprising a conductive material can bedisposed underneath the workpiece. The current collector forms anelectrical contact with the jet stream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The foregoing and other objects, features and advantages of thepresent invention, as well as the invention itself, will be made fullyunderstood from the following description and embodiments, when readtogether with the accompanying drawings, in which:

[0030]FIG. 1a shows a schematic view of an apparatus for cutting aworkpiece according to one embodiment of the invention.

[0031]FIG. 1b shows an inside view of the jetting head of FIG. 1aaccording to one embodiment of the invention.

[0032]FIG. 1c shows a detailed cross-sectional view of the nozzle areaof the jetting head of FIG. 1b.

[0033]FIG. 2a shows a workpiece for welding according to one embodimentof the invention.

[0034]FIG. 2b illustrates welding the workpiece of FIG. 2a according toone embodiment of the invention.

[0035]FIG. 3 shows a schematic view of an apparatus for cutting aworkpiece according to another embodiment of the invention.

[0036]FIG. 4a shows a cross-sectional view of the jetting head accordingto another embodiment of the invention.

[0037]FIG. 4b shows a detailed cross-sectional view of the nozzle areaof the jetting head of FIG. 4a.

[0038]FIG. 5a shows a detailed cross-sectional view of the jetting headaccording to another embodiment of the invention.

[0039]FIG. 5b shows a schematic view of an apparatus for cutting aworkpiece according to one embodiment of the invention.

DETAILED DESCRIPTION

[0040] In one aspect, the invention features a process and an apparatus,in which a workpiece is either cut or welded by an impinging, finestream of high temperature liquid metal working fluid. In oneembodiment, the liquid metal working fluid is formed by melting and thenholding the working fluid in a heated crucible. The temperature of themetal working fluid in the crucible is maintained at a temperature aboveits melting point. During operation, the working fluid is heated underpressure in the crucible and subsequently directed toward the workpieceas a jet stream passing through a nozzle orifice located at an outlet ofthe crucible.

[0041] In one embodiment, an electrical power source is connectedbetween the liquid metal working fluid in the crucible and anelectrically-conducting workpiece or an alternative electrode positionedbeneath the cut workpiece. During operation, an electric current ispassed between the liquid metal working fluid in the crucible and theworkpiece or the alternative electrode via the liquid metal stream. Thepassage of current through the small diameter liquid stream heats thejet stream by ohmic (I²R) power dissipation (where I represents theelectrical current and R represents the electrical resistance). Thetemperature increase of the stream, enroute to the workpiece, isdependent on: a) the electrical power input to the stream; b) the streammass flow rate; and c) the heat capacity (specific heat) of the liquid.Since the power input to the stream is an independent variable, whichmay be operator controlled, energy can be added to the stream toincrease its temperature, as desired. This reduces the high temperaturedemands from crucible construction materials and makes it feasible tocut or weld materials with high melting-point temperatures using workingfluids that have much lower melting points. High melting point workpiecematerials can be worked (either cut, welded or brazed) by addingwhatever temperature is required for the working fluid enroute to theworkpiece. For example, mild steel and stainless steel, which haveapproximate melting points of 1550° C. and 1400° C., respectively, canbe cut with low melting point working fluids such as aluminum or tinalloys, which have approximate melting temperature of 660° C. and 232°C., respectively, by adding whatever additional temperature is requiredby I²R power dissipation in the liquid metal stream.

[0042] As an illustration of the invention's improvement in the cuttingprocess, the following Table 1 compares the typical theoreticalcross-sectional power densities of the above mentioned cuttingprocesses. The cutting speeds and process parameters are assumed to betypical for each process. The power density is calculated for eachprocess as the energy passing through a cross-sectional diameter equalin size to the kerf width associated with each process. As can be seenin Table 1, the process of the present invention delivers, by far, morepower per unit area than any of the other processes. This power densityis an indication of the ability of the process of the present inventionto deliver melting energy to a workpiece kerf. TABLE 1 Typical PowerDensities (W/mm²) for Cutting Processes (cutting ½″ mild steel, 1520° C.melt temp) Cutting Process Power Density 1. Oxy-fuel (oxygen-ironburning reaction, 2 mm kerf) 14 2. Plasma (200 A, 100 V, 4 mm kerf)1,600 3. Laser (3 kW with oxygen assist, 0.4 mm kerf) 24,000 4. AluminumJet (200 μm nozzle, 14,600 1750° C. jet, 0.2 mm kerf) 5. Aluminum Jet w/I²R Heating (200 μm nozzle, 53,000 1750° C. jet + 1.2 kW I²R, 0.2 mmkerf) 6. Aluminum Jet w/ I²R Heating (200 μm nozzle, 30,000 900° C.jet + 2.1 kW I²R, 0.2 mm kerf)

[0043] As shown in the Table 1, the initial temperature of the aluminumjet (900° C.) can be less then the melting temperature of the workpiece(1520° C.), with the additional temperature needed to cut the workpiececoming from the added I²R power dissipation.

[0044] Referring to FIGS. 1a, 1 b, and 1 c, an apparatus for cutting orwelding a workpiece includes a jetting head (9), a crucible neater powersupply (34), a stream heating power supply (54), and a pressurizing gassource (22). The crucible power supply (34) is electrically connected tothe jetting head (9) through a pair of leads (32) (33). The streamheating power supply (54) is electrically connected to the jetting head(9) through a negative lead (52) and to a workpiece (70) through apositive lead (53). Gas from the gas source (22) is supplied to thejetting head (9) through a pressurizing gas source interconnectingpiping (18), a pressurizing gas source regulator (23), and apressurizing gas source on/off valve (20). The jetting head (9) isde-pressurized through a de-pressurizing vent (25), a de-pressurizingvent interconnecting piping (19), and a de-pressurizing vent on/offvalve (21).

[0045] The jetting head (9) includes a pressure containment vessel (10),a crucible (11), a crucible heater (30), a feedthrough (30 a) for thepair of leads (32) (33), a stream heating electrode (50), a feedthrough(50 a) for the negative lead (52), a plug rod (26), a plug rod actuator(26 c), a plug rod seal (26 e), a plug rod ball (26 a), a plug rod ballseat (26 b), a crucible compliant top seal (16), a crucible bottomsealing gasket (15), a nozzle disk (12), a nozzle disk sealing gasket(14), a nozzle nut (13) and a molten metal working fluid (80).

[0046] The feedstock (87) is fed into the jetting head (9) through thefeedstock inlet (17 c). The feedstock (87) can be introduced into thejetting head (9) in either solid form as shown, where the melting andliquid forming takes place in the crucible (11), or the feedstock can beintroduced in liquid form, where the melting and forming of the liquidmetal takes place outside of the jetting head (9), prior to itsintroduction into feedstock inlet (17 c). In either case, workingmaterial moves into the jetting head (9) through the feedstock passage(17 d) and into the crucible (11). During operation, the heated crucible(11) maintains the feedstock (87) in a molten state. The feedstock (87)is fed through the opening (17 e) in the feedstock valve (17) when theopening (17 e) is aligned with the passage (17 d). When closed byfeedstock valve actuator (17 b), the opening (17 e) no longer alignswith the passage (17 d), the passage (17 d) is then gas-tight sealed byseals (17 a). The feedstock valve (17) allows the interior of thejetting head (9) to be pressurized.

[0047] The crucible (11) is heated by the crucible heater (30). Thecrucible heater (30) can be any heater which heats the crucible (11) tothe desired temperature. For example, the heater (30) can be AC or DCresistance heater, an induction heater, or a combustion burner-heater.In one embodiment, an AC electrical resistance heater is used. Thisheater has power connections (32) and (33), which are, in turn connectedto the crucible heater power supply (34). Power leads (32) and (33) passthrough the pressure vessel top (10 b) via crucible heater electricalfeedthrough (30 a). This feedthrough (30 a) makes a gas pressure sealwith the pressure vessel top (10 b) and insulates the leadselectrically.

[0048] In one embodiment, the crucible (11) has side walls and a base.The crucible (11) is made of a refractory material, which is compatiblewith the high temperature molten working fluid so that the crucible isresistant to dissolving in the presence of a metallic melt. Examples ofsuitable crucible materials include, but are not limited to, zirconiumcontaining compounds, alumina and zirconia ceramics of variouscompositions, boron nitride materials of various compositions, boronnitride, boron nitride-zirconia-silicon carbide, silica, zirconiumdiboride, Yttria-Stabilized-Zirconia, Magnesia-Stabilized-Zirconia,Calcia-Stabilized-Zirconia, Cubic Zirconia, silica composites, andgraphite. In one embodiment, the crucible material can be boron nitridematerials, such as Grade ZSBN material, which is made up of boronnitride-zirconia-silicon carbide, supplied from The Carborundum Companylocated in Amhurst, N.Y. In another embodiment, the crucible is made ofgraphite. Since graphite is electrically conductive it may be desirableto electrically isolate the crucible (11) from the pressure containmentvessel (10) and the crucible heater (30). In one embodiment, thecrucible (11) is electrically isolated. The bottom end of the crucible(11) is sealed by the crucible bottom gasket (15) located on the bottomof the crucible (11), between the crucible (11) and the pressure vesselbottom (10 a). In one detailed embodiment, the gasket (15) is made ofhigh temperature alumina refractory gasket material, which is anelectrical insulator. The gasket (15) is loaded under pressure from thecompliant seal (16) located on the top of the crucible (11), between thecrucible (11) and the top of the pressure vessel (10 b).

[0049] In one embodiment, the outlet for the liquid metal working fluidis sealed by the movable plug rod ball (26 a), which is in a sealing fitrelationship with the plug rod ball seat (26 b). The plug rod actuator(26 c) applies a sealing force through arm (26 d) to the plug rod (26),which forces the plug rod ball (26 a) on to the plug rod ball seat (26b) during times of no liquid metal flow. Since the crucible (11), theplug rod (26), the plug rod ball (26 a) and the plug rod ball seat (26b) are in contact with the liquid metal (80), the construction materialsfor these components must be chosen so that they will withstand themechanical and thermal stresses at high temperature and resist corrosionin a chemically reactive environment. In addition, the plug rod ball (26a) and plug rod ball seat (26 b) must be made of materials which willtogether make a good intermittent seal of the liquid metal underpressure. It is anticipated that working pressures will range from about50 to about 5000 psi. In addition, in one embodiment, the plug rod (26)and the plug rod ball (26 a) are electrically isolated and/or made ofelectrically non-conducting material in order to electrically isolatethe working fluid resistance heating power supply (54) from othercurrent paths. The electrical isolation of the crucible and plug rodparts would not be necessary if the entire jetting head assembly wereallowed to ‘float’ electrically at the same potential as the crucible.The plug rod (26) is sealed on the pressure vessel top (10 b) by plugrod pressure seal (26 e).

[0050] In one embodiment, the stream-heating power source (54) isconnected to the working fluid (80) by an electrode (50) which extendsdown into the crucible (11) and is generally surrounded by and in goodelectrical contact with the liquid metal working fluid (80). Theelectrode (50) is connected to the power supply (54) by a connectingwire (52), which passes through the top (10 b) of the pressure vesselvia the feedthrough (50 a). This feedthrough (50 a) makes a gas pressureseal and electrical insulation with the top (10 b) of the pressurevessel. The opposite polarity of the stream heating power supply (54) isconnected via cable (53), switch (54 a) and electrical clamping means(55) to workpiece (70).

[0051]FIG. 1c shows an enlarged view of the nozzle area. The nozzle areaincludes a nozzle disk (12). The nozzle disk (12) is a cylindrical diskhaving a top (12 a), a bottom (12 b) and an outside diameter wall (12c). An orifice (5) is formed at the top (12 a) of the nozzle disk (12)on the centerline. The orifice (5) has a bore (5 a) and a length (5 b).A conical opening (5 c) extends from the outlet of orifice (5) to thebottom (12 b) of the nozzle disk (12). Typical orifice diameters canrange from about 25 to 500 μm. The nozzle disk (12), in one embodiment,is made out of a material which is electrically conductive and resistantto dissolving in the presence of a metallic melt, and the nozzle disk(12) can be formed with a precise, small diameter orifice and which canfunction in the severe environment of high temperature liquid metals.The nozzle disk (12), like the crucible (11) can also be made out ofzirconium containing compounds such as Yttria-Stablized-Zirconia,Magnesia-Stablized-Zirconia, Calcia-Stablized-Zirconia, boron nitride,boron nitride-zirconia-silicon carbide, Cubic Zirconia, Alumina, Silica,Silica Composites, Zirconium Diboride. In one detailed embodiment, thematerial for the nozzle disk (12) is sapphire (e.g., alumina). Thenozzle disk (12) is held against the nozzle sealing gasket (14) bypressure applied by a nozzle cap (13). The nozzle cap (13) has athreaded portion (13 a) which is attached to the bottom (10 a) of thepressure vessel on threaded portion (10 c). In one embodiment, thenozzle sealing gasket (14) is made of a material which can function inthe severe environment of high temperature liquid metals. For example,the gasket material can be graphite, such as the ‘Calgraph™’ materialsupplied by SGL Technic Inc. of Valencia, Calif.

[0052] The outside boundary of the jetting head interior is defined bythe inside wall of the pressure containment vessel (10). This pressurevessel (10) must be made of material which can maintain high strength athigh pressure and elevated temperature, such as ‘Inconel™ 600’, which isa high nickel, super alloy available from the Inco Alloys InternationalCo. The pressure containment vessel (10) is pressurized through apressurizing gas source piping (18) which is connected to thepressurizing regulator (23) and the pressurizing gas source (22). Anon/off valve (20) is located some where along the pressurizing gassource piping (18). The pressure containment vessel (10) isde-pressurized through the de-pressurizing gas vent piping (19) which isconnected to the de-pressurizing gas vent (25). An on/off valve (21) islocated somewhere along the de-pressurizing gas vent piping (19). Theembodiment of FIG. 1b is designed so that the walls of the hightemperature crucible are not subjected to the high stresses caused bythe periodic pressurization of the jetting head (9). This isaccomplished by allowing the pressurizing gas flow to have access toboth the inside wall (11 a) and the outside wall (11 b) of the crucible(11). The pressurizing gas is allowed to flow freely through gaspassages (11 c) of the crucible (11). The internal cavity (8), which isall of the free space in the jetting head between the outside ofcrucible (11) and the interior walls of the pressure containment vessel(10) acts as a very effective thermal insulation barrier. This space,however, acts as a gas capacitance when charging and discharging thevessel with high pressure. In order to minimize this capacitance, theinternal cavity (8) may be filled with a non-porous thermal insulation.

[0053] In one embodiment, feedstock (87) is fed into the jetting head(9) during times when the jetting head is not under pressure. Thefeedstock is held in crucible (11) and is then melted if the feedstockis fed in as a solid, and is maintained in molten state.

[0054] When the jetting head (9) is powered up, in preparation forcutting, the crucible power supply (34) is turned ‘ON’ by closing switch(34 a), thus supplying power to the crucible heater (30). The crucibleheater (30) will, by controls not shown, maintain the temperature of theworking fluid (80) at a predetermined temperature somewhere above itsmelting point. The predetermined temperature is set by electronicmonitoring controls which use feedback from temperature sensors locatedin or near the molten metal working fluid. This electronic controlsystem and temperature sensors are not shown but are commerciallyavailable.

[0055] In one embodiment, an induction heater is used as a crucibleheater (30). The induction heater can detect changes in the level of themolten metal working fluid in the crucible. A characteristic frequencyof the induction heater changes with the level of the molten metalworking fluid. In an induction heater, the material to be heated iscoupled to the heater's coil by the magnetic fields inside the coil. Thepresence of the material and of the eddy currents induced in thematerial interact with and change the magnetic fields from the coilcompared to what the fields would be without any material inside thecoil. The additional impedance of the material changes the totalimpedance of the coil. The change in impedance of the coil changes the Qof the circuit and its resonant frequency. Therefore, the inductionheater would operate at different frequencies for conditions wherematerial is present or absent inside the coil. Similarly, varyingamounts of material inside the coil would result in varying shifts infrequency. The characteristic frequency can be monitored and calibratedto measure the level of the molten metal working fluid.

[0056] The molten metal working fluid (80), which is formed from thefeedstock (87) is specifically chosen for the particular application ofinterest. Although the working fluid is referred to as ‘metal’ theworking fluid can, in fact, be any electrically conductive fluid whichwill produce the desired effects on the workpiece. Some materials thatcan be used for the feedstock (87) include mild steel, aluminum,aluminum alloy, tin, stainless steel, iron, cast iron, tool steel,copper, zinc, gold, silver, nickel, titanium, magnesium or platinum. Forexample, when the desired effect is to cut mild steel or stainlesssteel, the working fluid may be an aluminum or aluminum-iron alloy.

[0057] Aluminum and aluminum alloys have several properties that makethem good choices for the working fluid; such alloys have low meltingpoint temperature, high boiling point temperature, high specific heatcapacity, high thermal conductivity and, a relatively low cost perkilogram. The melting point of pure aluminum is approximately 660° C.,the melting point of aluminum-iron alloys (or metal mixtures) vary fromapproximately 660° C. to 1540° C. depending on the amount of iron in themixture. The melting point of an aluminum-iron mixture with 90% aluminumcontent is approximately 800° C.

[0058] A major benefit of the present invention is the ability to use aworking fluid at such temperatures because it makes possible the use ofa number of available refractory materials for the crucibleconstruction. Because pure iron melts at about 1540° C., it is obviousthat additional temperature must be added to the stream, enroute toworkpiece in order to cut. In addition, there is another benefit ofusing aluminum or aluminum alloys as the working fluid. That is, thetemperature of an aluminum-iron alloy has a lower melting temperaturethen pure iron (or steel). Therefore, to the extent that the alloyingprocess speed is fast enough, there will be this additional alloyingprocess mechanism helping the cutting process when the stream combines(alloys) with a higher melting point workpiece metal. The alloyingprocess, in general, will help the cutting process of all workpiecemetals with melting points higher then that of the cutting stream by, ineffect, lowering the melting point temperature of the workpiece metal incontact with the cutting (and alloying) stream.

[0059] As another example, a stainless steel workpiece could be cutusing a working fluid which consists of a compound material, such as, analuminum-magnesium alloy which also contains disperse amounts of fineceramic particles, such as 0.5-25 μm alumina or zirconia particles. Thiscutting fluid has the advantage of having non-melting particlesdispersed throughout the fluid to serve as abrasives to assist in thecutting process.

[0060] The present invention is not limited to be used with low meltingtemperature metal as the working fluid. For example, a mild steelworkpiece can be cut with a mild steel, a cast iron, a tool steel or apure iron working fluid. This choice of cutting fluid has thedisadvantage of a high melting point. However, there are a few cruciblematerials which can withstand temperatures around the melting point (orfluidization) temperature of iron and since any temperature above themelting point that is required can be added outside of the crucible,with the I²R power dissipation, the use of pure iron as cutting fluid ispossible in the present invention, and may be desirable in some cases.One benefit of using a mild steel or iron as a cutting fluid is thatenroute oxide formation will not adversely affect the fluidity of thestream; iron oxide has a lower melting point then iron itself. Some highcarbon steels have melting points less then that of pure iron which,therefore, make them candidate choices for cutting fluids. Other choicesfor cutting fluids for use in cutting mild steel include AISI 1006through AISI 1095 steels, cast irons, and tool steels. In anotherexample, if the workpiece to be cut is an aluminum alloy such as 6061,the working fluid can be a pure aluminum or an aluminum alloy. As stillanother example, if the workpiece to be cut is tin, the working fluidcan be tin. In general there may be an advantage for the working fluidmaterial to be the same material as the workpiece. For example whencutting, there would be no discernable metallurgical differences betweenthe base metal of the workpiece and the metal on the cut face. Inanother example, when cutting 316 stainless steel there would be anadvantage in using 316 stainless steel as the working fluid material inthat the same alloying elements would exist through-out with no changein the area of the cut.

[0061] Just prior to the beginning of a cutting operation, the followingconditions exist: a) the plug rod actuator (26 c) is in the offcondition and the plug rod ball (26 a) is sealing against the plug rodball seat (26 b); b) the feedstock valve (17) is closed and valve seals(17 a) are sealing passage (17 d) from the outside environment; c) thede-pressurizing gas venting valve (21) is in the ‘off’ condition and theventing path is closed; d) the pressurizing gas valve (20) is in the‘off’ condition and the gas path to the pressurizing gas source isclosed, and the pressurizing gas source is ready to supply gas to thejetting head; e) crucible heater power supply (34) is in the ‘on’condition, switch (34 a) is closed, and crucible heater (30) issupplying heat to crucible (11); f) the stream heating power supply (54)is turned ‘on’ and switch (54 a) is closed so that the power supply isapplying an electrical potential between the liquid metal fluid (80) andthe workpiece (70).

[0062] The cutting operation is accomplished by first opening thepressurizing gas source valve (20) which pressurizes the interior of thepressure vessel (10), including the inside of the crucible. Thepressurizing gas is selected to be non-oxidizing and inert to reactionswith the molten metal. Possible choices for the pressurizing gas includeargon, nitrogen, helium, and argon with some hydrogen. In oneembodiment, the pressurizing gas is argon with 5% hydrogen added. Thepurpose of the hydrogen is to make the pressurizing atmosphere slightly‘reducing’ in order to inhibit oxide formation. A special benefit ofusing iron as the working fluid is that the presence of oxygen in thepressurizing gas will not adversely affect the fluidization processsince iron oxide, if formed, will be fluidized along with the pure iron.The presence of oxygen may, however, be undesirable for other componentsof the jetting head such as the crucible and/or sealing gaskets.Subsequently, the plug rod actuator (26 c) is energized, which lifts byplug rod (26). The plug rod ball (26 a) is thereby lifted from the seat(26 b). As shown in FIG. 1c, liquid metal fluid (80) flows throughnozzle orifice (5), forming a stream of liquid metal (82). When thestream contacts the workpiece (70), current will immediately begin toflow from the stream heating power supply (54) through the stream (82).This current flow immediately raises the stream temperature. As the hightemperature stream impinges on the workpiece, it melts and erodes a pituntil finally the heated stream penetrates all the way through theworkpiece. At this point the workpiece has been pierced by the jet. Thenfinally relative movement (72) between the workpiece and the jettinghead is started. These actions together cause the workpiece to be cut.The relative movement continues until the desired shape has been cut. Atwhich point the relative movement can be stopped and stream (82) can beturned off by: a) opening switch (54 a) which stops the current flowthrough the stream; b) de-energizing actuator (26 c) which lowers plugrod (26), forcing plug rod ball (26 a) on to seat (26 b); c)de-energizing (closing) the pressurizing valve (20); d) energizing(opening) venting valve (21) which allows the pressurizing gas to flowout of the pressure vessel (10) through vent (25). The cutting sequenceis then reset for the next cut by again closing switch (54 a) so thatthe power supply is applying an electrical potential between the liquidmetal fluid (80) and the workpiece (70). When it is desired to make thenext cut the same sequence as above is followed. During a cutting orwelding process the current flowing through the jet to the workpiece cansometimes form a plasma arc at or near the workpiece surface. Thisplasma arc formation can be detrimental to the cutting or weldingprocess and may cause the process to become erratic resulting in poorcut or weld quality. It is important that steps be taken in controllingof the cutting or welding process to limit the arcing to a very minimum,or if possible, totally eliminate the arcing. One such step is to ensurethe quality of the jet stream by employing filters to the working fluidprior to forming the jet. Filters for molten metals are commerciallyavailable. For example, filters for made of a typical composition of 93%zirconia, 5% magnesia and <2% alumina-silicates and other compounds aremade for mild steel filtering and are available form the SELEE Corp ofHendersonville, N.C.

[0063] The following table summarizes results from cutting variousmaterials using tin jet in accordance with the present invention. TheI²R power was added to the tin jet via a DC power supply. Liquid MetalJet Cutting with Added I²R Heating Tin jetting material 250 microndiameter nozzle 400 C. vessel temperature 400 psi vessel pressureMaterial Material Power Current Cut Speed Stand-Off Cut Thickness [m][w] [A] [m/min] [m] Tin 0.00635 714 54.9 14.8 0.016 Aluminum 0.006352500 75.3 3.8 0.022 Mild Steel 0.003175 1500 63.4 0.2 0.022 Stainless0.003175 2100 86.0 0.25 0.016 Steel

[0064] In another aspect, the present invention is directed to a weldingapparatus and a method of welding a workpiece using the apparatus ofFIGS. 1a-1 c. The stream is additionally heated by I²R energydissipation to elevate its temperature to a useful temperature forwelding. Choice of filler material (working material stream) isselected, just as a specific welding rod is chosen in conventionalwelding. The stream velocity (which is governed by the pressure inpressure vessel), the diameter of the nozzle orifice and the orientationof the jetting head to the workpiece and stream temperature (I²R powerdissipation) would be adjusted to set the depth of penetration. Becausethe stream velocity and thus mass flow rate can be varied from very highto very low values, the filler material can be added in much the samemanner as wire in a conventional MIG welding processes, i.e., in azig-zag (weaving) fashion. This allows a wider path of penetration inworkpieces. FIG. 2a shows two pieces of metal (74 a and 74 b) pieceswhich have been prepared for a fillet type weld. Both (74 a) and (74 b)have tapered edges (74 c) which are to be welded together. When thetapered edges are placed in the proper position for welding, the taperededges form a groove (74 d).

[0065]FIG. 2b illustrates a welding process using an apparatus of thepresent invention.

[0066] Referring to FIG. 2, jetting head (9) and emanating stream (82)are directed toward the workpieces. The stream (82) makes contact withthe two workpieces (74 a) and (74 b) somewhere in groove (74 d) alongone of the tapered edges (74 c). After contact is made, electric currentflows through the stream (82), the workpieces (74 a) and (74 b), andback to the stream heating power supply (54) (not shown in FIG. 2b)through clamp (55) and lead (53). The stream (82) is heated by I²R powerdissipation, the same as in the case of cutting. As the I²R heatedstream is moved along in relative motion (76) it heats and meltslocalized portions of edges (74 c) as the workpieces (74 a) and (74 b)are being welded together. As the workpieces melt, a molten pool (75 a)is formed by the molten portions of the workpieces and by the metalstream (82). Metal is continuously added to the pool by the stream (82).The amount of material added is controlled by the stream velocity (82 a)and diameter. As weld (75) progresses, some distance behind the weldpool, the welded area begins to cool below the weld area melting pointand solidifies. Although not shown, welding processes will always havesome form of shielding gases flowing around the weld area. Theseshielding gases protect the weld area from oxygen and other undesirableatmospheric contaminants such as nitrogen. Also, the process of thepresent invention allows for the addition of fluxing types of materialsto the working fluid to improve the welding process, either added to theworking fluid while in the heated crucible, or added to the feedstock(87) as an additive compound or laid down as powder as in submerged-arcwelding.

[0067] In one embodiment, cutting of non-metallic, non-conductive, andinsulating materials can be accomplished by allowing the molten streamto collect in an electrically conductive pot as shown in FIG. 3. In thisembodiment, it is not necessary for the workpiece to be electricallyconductive. The current path for the stream heating is the same as inFIGS. 1a-1 c except now the current flows through the stream (82), intothe current collection material (83), through current collection vessel(57), through clamp (56) and back through lead (53) to power supply(54). The current collection material (83) can be completely molten oronly partially molten and is made up generally of both the streammaterial and the workpiece material. Additional current collectingmaterial (83) could be added to the current collection vessel (57)separately from the cutting process. An important feature of the currentcollecting material (83) is that it makes good electrical contact withthe stream (82). The I²R heat addition to the stream would still takesplace. The temperature of the stream at the top surface of the workpiececan be controlled, as in the embodiment, by the choice of working fluid,the amount of current passing through the stream, the flow rate of thestream, the diameter of the stream and the length of the stream from theworkpiece to the inlet to the nozzle orifice (5). Workpiece (70) isbeing cut as it passes through the I²R heated stream (82) with relativemotion (72) between the jet head (9) and the workpiece (70). Thisdiffers from the embodiment in that the work piece is not part of theI²R heating circuit.

[0068] In another embodiment, an induction heated crucible, as shown inFIG. 4a, is used as a possible variation of the implementation of theinvention. In this variation of the jetting head, the crucible heater(30) is replaced with induction heater coils 35 with an incoming coiltube (35 a) and an outgoing coil tube (35 b). The induction heater powersupply and its cooling system (not shown), are used in this embodiment.Also incorporated into the implementation shown in FIG. 4a is the methodof stopping the working fluid flow by use of a levitating force appliedto the working fluid (80) by the induction forces caused by the heatingcoil (35). When a conducting working fluid is placed in an inductionfield, the induced current heats the metal conductor. It also creates anopposing magnetic flux that tends to push the metal working fluid into aregion of lower field strength, i.e., out of the field (or coil). Thispushing force may be computed using the ‘Lorentz’ equation. If theinduced magnetic field is uniform, there is no net force on the workingfluid. A field gradient is needed to provide a lifting force. In oneembodiment, this is accomplished by forming the coil (35) in a conicalshape with the coils near the lower end of the crucible being smaller indiameter then the coils near the upper end of the crucible. In anotherembodiment, this is accomplished by forming the coil (35) with the coilnear the lower end of the crucible in a closer packed relationship thanthe coil near the upper end, as shown in FIG. 4a. This levitating forcecreates a lifting (or levitating) force on the liquid metal fluid whichovercomes the force of gravity acting on the liquid metal, preventing itfrom dripping or leaking. In this design, the stopping of stream (82) iscaused by a combination of changing the pressure in pressure vessel (10)and the applied levitating force of the induction coil; there is no needfor the plug rod (26) arrangement of the embodiment shown in FIG. 1b.The nozzle area is shown in FIG. 4b in the condition of no flow. FIG. 4bshows the liquid to be held in the nozzle orifice without exiting. Thisis due to the levitating forces of the operating induction coil (35).

[0069] Also, shown in the embodiment in FIG. 4b is an improvement to theprocess by the addition of gas shielding at the nozzle exit. In thisembodiment, a nozzle disk (12) is held in position by the assemblyconsisting of a shield gas disk (29 a), a down stream portion (29 b),and springs (29 c). Shielding gas flow (27) is applied to the nozzleexit area (29). Shield gas flow (27) flows from the shield gas source(not shown) and flow regulator (not shown) through an on/off valve (28)and connecting lines (28 a) and (28 b) to the nozzle area (29) throughholes (29 d) in the shield gas disk (29 a). The main benefit of gasshielding is to reduce the effects of ambient air on both the workingfluid stream (82) and on the workpiece(s). Although this shielding isnot shown in the embodiment of FIG. 1b it is contemplated that thisfeature would most likely be applied to the embodiment.

[0070] In another embodiment, an induction heated crucible and afeedstock heater, as shown in FIGS. 5a and 5 b, are used as a possiblevariation of the implementation of the invention. In this variation ofthe jetting head, the crucible heater (30) is replaced with inductionheater coils 35, with an incoming coil tube (35 a) and an outgoing coiltube (35 b). The induction heater power supply and its cooling system(not shown), are used in this embodiment. Feedstock wires or rods 87 aand 87 b are fed through electrical contacts 42 a and 43 a and throughpressure seals 45 a and 45 b. Contacts 43 a and 42 a are electricallyconnected electrical connection wires 43 and 42 respectively. Wires 42and 43 are connected to the positive and the negative contacts of powersupply 44. The feedstocks 87 a and 87 b are electrically connectedtogether by driving them down into the conductive fluid 80 contained incrucible 11. The feedstocks 87 a and 87 b are heated resistively byclosing contact switch 44 a of power supply 44. By allowing this initialI²R heating 20 of the feedstock 87 a and 87 b, via power supply 44, theoverall power requirement for the induction heater 35 is reduced. Thejet heating power supply 54 is connected to the workpiece 70 via clamp55 and cable 53, through switch 54 a, and is connect to the jet 82 viacable 52, which is connected to power supply 44 via cable 43, which isin-turn connected to the conductive fluid via contact 43 a and feedstock87 b. It is of course understood that power supply 54 could have beenconnected to the conductive fluid through cable 42 and the otherfeedstock 87 a in the same manner as described.

[0071] In one embodiment, a filter 47 is placed in series with thejetting nozzle, the conductive fluid flows first through the filter andthen flows to the nozzle where the jet is formed.

[0072] In one embodiment, in place of using a plug rod (26), sealingball (26 a), and actuator (26 c) to prevent fluid flow during the “off”condition, a vacuum source is used to create a “suction” inside thevessel which would overcome the force of gravity acting on the liquid,preventing it from dripping or leaking.

[0073] In another embodiment, reversing the polarity of the streamheating power supply (54), or using AC power may prove useful insuppressing observed arcing and sparking on the workpiece surface, andminimizing workpiece oxidation.

[0074] In another embodiment, the present invention features methods ofintroducing the cutting fluid feedstock (87) into the pressure vessel(10) of the jetting head (9) including feeding the feedstock as eitherrod, wire, powder, or liquid metal. In one example, the feedstock isintroduced into the pressure vessel under the full operating pressure.

[0075] In one embodiment, the invention features using an electricalcurrent flow in a stream (jet) of metal to raise the stream temperature.In one example, the invention features the use of the liquid metal jetwith added current (I²R heating) for the purposes of cutting andwelding.

[0076] In one embodiment, the invention features the use of pure metalsas the cutting fluids, including iron, aluminum, tin, nickel, titanium,gold, platinum, silver, magnesium, and copper, in combination with theI²R heat addition process.

[0077] In one embodiment, the invention features the use of low meltingtemperature metals having high boiling point temperatures for thecutting fluid, in combination with the I²R energy addition process.Examples of suitable cutting (working) fluid include but are not limitedto: aluminum and aluminum alloys; tin and tin alloys.

[0078] In one embodiment, the invention features the use of thebeneficial effects of alloying in the cut, which reduces the meltingtemperature of the workpiece in the vicinity of the metal jet and kerffront, in combination with the I²R heating process.

[0079] In one embodiment, the invention features the use of non-meltingadditions to the working fluid, such as, ceramic particles andrefractory metal particles, which would help the cutting process byabrasion and enhancing heat transfer by stirring the interaction zone ofthe jet with the kerf front. The size of particles could range fromabout 0.2 to about 20 microns.

[0080] In one embodiment, the invention features the use of thelevitating force of induction to stop the liquid metal fluid flow fromthe crucible.

[0081] In one embodiment, the invention features the technique ofseparating the high pressure requirement of a holding vessel from thehigh temperature requirement. This is done by placing both the holdingvessel (crucible) and its heating source in the pressurizingenvironment.

[0082] In one embodiment, the invention features a technique of cuttingnon-metals or, in general, non-electrically conducting materials usingthe I²R heated liquid stream and by make the electrical connections tothe stream at the up-stream side by contact to the working fluid in thepressure vessel (crucible) and on the down-stream side by contact by thestream to a separate current collection means located beneath theworkpiece.

[0083] In one embodiment, the invention features the use of the presentinvention for the purpose of ‘Surface Cladding’ or ‘Surface Welding’,wherein a workpiece is coated (or cladded) with the working fluid. Theworking fluid stream is manipulated so as to coat the workpiece with theworking fluid.

[0084] In one embodiment, the invention features the use of the presentinvention for the purpose of ‘3-D Forming’, wherein a three dimensionalstructure is built-up (or formed) from the working fluid. The workingfluid stream is manipulated under computer-code control, so as to builda freestanding, three dimensional structure with the working fluid. Oneprincipal reason why liquid metal jet presents a significant advantageover existing techniques in welding, coating, and forming is that theworking material is liquid. This permits liquid of unique composition tobe formulated in the crucible by supplying several types of feed mixturecan be varied over a much larger range than in the solid state. Whenthis liquid is rapidly cooled to the solid phase at rates of 10³-10⁶K/sec, an alloy with non-equilibrium composition is produced. Thiscomposition can be tailored to create solid materials with uniqueproperties not generally available in conventional materials. As anexample, special magnetic properties can be created in Fe-alloys.High-strength aluminum (and other lightweight metal) alloys can be madethis way due to the refined grain structure that is produced. This isthe technique that gas-assist metal atomization processes use to produceexotic metal powders that are used in the powder metal and thermal sprayindustry. The process of rapid cooling/rapid solidification of liquidmetals is known to those skilled in the art.

[0085] The ability to accurately control the location and size of thedeposition spot of the liquid metal jet (apparently, within microns) isan exceptional advantage when compared to existing spray technology thatuses gas jets and powder. Such techniques produce deposition spot sizeson the order of millimeters and suffer from overspray and low depositionefficiency.

[0086] Furthermore, the liquid metal jet diameter may be madesufficiently small (10's-100's of microns) that rapid cooling rates onthe order of 10³-10⁶ K/sec (often referred to as splat cooling) may beachieved. The approximate dimensions of the solidified metal depositresulting from a single pass of the liquid metal jet over a surface maybe estimated from droplet flattening and solidification models. Stillanother advantage of the liquid metal jet is the ability to incorporateparticulate, or perhaps even fiber reinforcement into the deposit. Theparticulate may be introduced into the molten metal in the crucible, orthey may be co-deposited by a second gas jet to the deposition site.

[0087] Equivalents

[0088] While the invention has been particularly shown and describedwith reference to specific refered embodiments, it should be understoodby those skilled in the art that various changes in form and detail maybe made therein without departing from the spirit and scope of theinvention. For example, other methods of increasing a temperature of ametal jet in addition to those described herein can be used inaccordance with the present invention to modify a workpiece.

1. A metallic liquid jet cutting system for modifying a workpiececomprising: a dispenser for dispensing a jet stream of an electricallyconductive fluid; and a power source electrically coupled to the jetstream.
 2. The system of claim 1 wherein the dispenser comprises ajetting head.
 3. The system of claim 2 wherein the jetting headcomprises a crucible
 4. The system of claim 3 wherein the cruciblecomprises a top, a sidewall, and a bottom, wherein the top comprises aninlet and the bottom comprises an outlet.
 5. The system of claim 3wherein the crucible comprises one of boron nitride-zirconia-siliconcarbide, Yttria-Stabilized-Zirconia, Magnesia-Stabilized-Zirconia,Calcia-Stabilized-Zirconia boron nitride, Cubic Zirconia, alumina,silica, silica composites and zirconium diboride.
 6. The system of claim3 further comprising a heater coupled to the crucible
 7. The system ofclaim 6 further comprising a second power supply electrically coupled tothe heater.
 8. The system of claim 2 wherein the jetting head comprisesan inlet for receiving a feed stock of the conductive material.
 9. Thesystem of claim 1 wherein the conductive material comprises mild steel,aluminum, aluminum alloy, tin, stainless steel, iron, cast iron, toolsteel, copper, zinc, gold, silver, or platinum.
 10. The system of claim2 wherein the jetting head comprises a pressure containment vessel. 11.The system of claim 2 wherein the jetting head comprises an electrodedisposed inside the crucible for establishing an electrical connectionwith the jet stream.
 12. The system of claim 11 wherein said electricalconnection comprises a feedstock of conductive material.
 13. The systemof claim 2 wherein the jetting head comprises an exit orifice.
 14. Thesystem of claim 2 wherein the jetting head further comprises a nozzle.15. The system of claim 14 wherein the nozzle comprises a disk having athrough orifice.
 16. The system of claim 15 wherein the disk comprises amaterial selected from one of Yttria-Stablized-Zirconia,Magnesia-Stabilized-Zirconia, Calcia-Stabilized-Zirconia, boronnitride-zirconia-silicon carbide, boron nitride, Cubic Zirconia,Alumina, Silica, Silica Composites, Zirconium Diboride.
 17. The systemof claim 15 wherein the through orifice comprises a circular crosssection.
 18. The system of claim 6 wherein the heater comprises one ofan AC resistance heater, a DC resistance heater, an induction heater, ora combustion burner-heater arrangement.
 19. The system of claim 3wherein the crucible comprises a refractory material.
 20. The system ofclaim 3 wherein the crucible comprises ceramic material.
 21. The systemof claim 3 wherein the crucible comprises a material selected from oneof alumina, zirconia, boron nitride, and graphite.
 22. A metallic liquidjet cutting system comprising: a jetting head including an inlet forreceiving a feed stock of a conductive material and an exit orifice fordispensing a jet stream of a conductive fluid; a heater coupled to thejetting head; and a power source electrically coupled to the jet streamfor providing a current to the jet stream to increase a temperature ofthe jet stream.
 23. A process for modifying a workpiece comprising: (a)providing a jet stream comprising a conductive fluid; (b) coupling anelectrical current into the jet stream; and (c) directing the jet streamto the workpiece for modifying the workpiece.
 24. The process of claim23 wherein step (b) comprises heating the jet stream by passing theelectrical current through the jet stream.
 25. The process of claim 23wherein step (a) comprises (a1) providing a feed stock of the conductivefluid, (a2) heating the feed stock to form the conductive fluid; and(a3) passing the conductive fluid through an exit orifice, therebyforming the jet stream.
 26. The process of claim 23 wherein step (a)comprises providing one of a continuous jet stream, a pulsed jet stream,a steady jet stream, or a unsteady jet stream.
 27. The process of claim23 wherein the feed stock comprises a wire, bar, or powder.
 28. Theprocess of claim 23 further comprising the step of (d) lowering amelting point of the workpiece.
 29. The process of claim 28 wherein step(d) comprises lowering the melting point by forming an alloy of the feedstock.
 30. The process of claim 25 wherein the feed stock comprises oneof iron, aluminum, tin, nickel, titanium, gold, platinum, silver,magnesium, and copper.
 31. The process of claim 23 wherein theconductive fluid comprises a low melting point of less than 1000° K anda high boiling point higher than 2500° K.
 32. The process of claim 25wherein the feed stock comprises a plurality of non-melting particles.33. The process of claim 32 wherein the non-melting particles areabrasive.
 34. The process of claim 23 wherein step (c) comprises one ofcutting, marking, piercing or welding the workpiece.
 35. The process ofclaim 23 wherein step (b) comprises applying a current to the jet streamthrough an electrode coupled to the conductive fluid and a currentcollector disposed near the workpiece.
 36. The process of claim 23wherein step (a) further comprises providing a levitation force to theconductive fluid to plug the exit orifice.
 37. The process of claim 25wherein step (a1) comprises providing the feed stock in a jetting head.38. The process of claim 25 wherein step (a3) comprises passing theconductive fluid through a nozzle.
 39. The process of claim 23 furthercomprising providing a shielding gas to the jet stream
 40. The processof claim 25 wherein step (a3) comprises pressurizing the jetting headwhile passing the conductive fluid through the exit orifice.
 41. Theprocess of claim 25 wherein step (a3) comprises pressuring the jettinghead by supplying an inert gas.
 42. The process of claim 23 wherein step(b) comprises heating the jet stream through ohmic power dissipation.43. The process of claim 23 wherein step (b) comprises heating the jetstream to a temperature substantially above a melting temperature of theconductive fluid.
 44. The process of claim 23 wherein step (c) comprisescontrolling a depth of penetration of the jet stream on the workpiece.45. The process of claim 23 wherein step (c) comprises adjusting avelocity of the jet stream.
 46. The process of claim 25 wherein step(a3) comprises controlling a pressure in the jetting head.
 47. Theprocess of claim 25 wherein step (a2) further comprises controlling atemperature of the conductive fluid.
 48. The process of claim 23 furthercomprising moving the workpiece relative to the jet stream.
 49. Theprocess of claim 23 further comprising providing a current collectorcomprising a conductive material disposed underneath the workpiece, thecurrent collector forming an electrical contact with the jet stream. 50.The process of claim 25 wherein the feed stock and the workpiececomprise a same material.
 51. The process of claim 25 wherein the feedstock and the workpiece comprise different materials.
 52. A crucible fora metallic liquid jet cutting system, wherein the crucible comprisesside walls and a base, the crucible being formed of a zirconiumcontaining compound that is electrically conductive and is resistant todissolving in the presence of a metallic melt.
 53. The crucible of claim52 wherein the metallic melt comprises one of iron, iron containingcompound, and aluminum.
 54. The crucible of claim 52 wherein thecrucible comprises one of zirconia diboride andyitria-stabilized-zirconia.
 55. A nozzle for a metallic liquid jetcutting system, wherein the nozzle comprises a disk-structure having anorifice, wherein the orifice is located at a center of thedisk-structure, the nozzle being formed of a zirconium containingcompound that is electrically conductive and is resistant to dissolvingin the presence of a metallic melt.
 56. The nozzle of claim 55 whereinthe metallic melt comprises one of iron, an iron containing compound,and aluminum.
 57. The nozzle of claim 55 wherein the nozzle compriseszirconium diboride.
 58. The process of claim 25 wherein the feedstock isone of tin, aluminum, iron, and mild steel.
 59. The system of claim 8wherein the jetting head comprises at least two inlets for receivingmultiple feedstocks of the conductive material.
 60. The system of claim59 wherein a third power source is connected to at least one feedstock.61. The system of claim 6 wherein the heater is an induction heaterhaving a characteristic frequency that can be calibrated to the level ofthe conductive fluid.
 62. The process of claim 23 wherein step a)further comprises filtering the conductive fluid.
 63. The system ofclaim 3 wherein the crucible further comprises a conductive fluidfilter.